OPTIONAL SYNTHESIS OF 2-OR 5-SUBSTITUTED 3-BROMOPYRROLES VIA BROMINE-LITHIUM EXCHANGE OF N-BENZENESULFONYL-2,4-DIBROMOPYRROLE

[摘要]：The regioselective bromine-lithium exchange of N-benzenesulfonyl-2,4-dibromopyrrole (6) with n-BuLi followed by treatment with various electrophiles gave 5-substituted 3-bromopyrroles (5) in excellent yields. In contrast, the sequential treatment of 6 with n-BuLi and diisopropylamine followed by quenching with electrophiles produced regioisomeric 2-substituted 3-bromopyrroles (3) selectively. The latter reaction can be rationalized by the rapid equilibration of the C-5 lithio species (4) to the more stable C-2 lithio species (2) in the presence of diisopropylamine.

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